The starting materials for producing bone cement, namely a pulverulent polymer and a liquid monomer, must be mixed directly before the introduction of the bone cement into the bone. This mixing procedure must therefore be carried out in the operating theatre under sterile conditions.
Different devices have been disclosed for this purpose, a common feature of these being that a mixing cylinder, in which the pulverulent polymer and the liquid monomer are mixed, serves immediately thereafter as a discharging cylinder or cartridge from which the ready-mixed bone cement is pressed out and brought to the application site.
A vacuum is normally generated in the mixing cylinder, either during the mixing procedure or directly thereafter, in order to reduce, at least to a substantial extent, the formation of pores in the bone cement.
In a known device of the generic type mentioned in the introduction (DE 43 02 230 A1), incorporated herein by reference, the starting materials, namely powder and liquid, must be introduced into the mixing cylinder prior to the mixing procedure, and only then is the mixing cylinder closed. By activating the mixing plunger by means of the actuation rod, the materials in the mixing cylinder are thoroughly mixed, during which the discharging plunger is held securely at the cylinder end. When the mixing procedure has been completed, the discharging plunger is released and is pressed as a press plunger into the mixing cylinder. The mixed bone cement is discharged at the opposite cylinder end. In the case where liquid and in particular powder are poured in freely, there is the risk of this material getting into the surrounding environment and leading to contamination, which is undesirable especially under operating conditions. Of particular concern in this respect is the possibility that the powder may lead to dust developing while it is being poured in, and that the liquid monomer may emit vapours. For this reason, it is necessary to pour the starting materials into the mixing cylinder as far away as possible from the operation site.